For analysis of samples, for example body fluids such as blood or urine, test element analysis systems are often used in which the samples to be analyzed are present on a test element and, if appropriate, react with one or more reagents on the test element before they are analyzed. Optical, in particular photometric, evaluation of test elements is one of the most common methods of rapid determination of the concentration of analytes in the sample. Photometric evaluations are generally used in the fields of analysis, environmental analysis and, above all, in medical diagnostics.
There are different kinds of test elements. For example, substantially square slides are known in the middle of which a multilayer test field is located. Diagnostic test elements of strip shape are referred to as test strips. Test elements are widely described in the prior art, for example in documents DE-A 197 53 847, EP-A-0 821 233, EP-A 0 821 234 or WO 97/02487. The capillary gap test elements also known from the prior art are test elements in which the sample liquid is conveyed from a sample application site to a remote sample detection site with the aid of capillary forces in a transport channel (capillary channel, capillary gap) in order to undergo a detection reaction there.
EP-B1 0 596 104 discloses a diagnostic assay device with a diagnostic element comprising a capillary space through which a reaction mixture flows, and a non-absorbent surface which is able to immobilize at least one target ligand from the reaction mixture in at least one zone, the non-absorbent surface having particles immobilized thereon which comprise an immobilized receptor. This assay device contains a time gate which comprises at least one hydrophobic zone in the capillary space that delays the flow through the capillary space to the at least one zone until the hydrophobic zone is made sufficiently hydrophilic through binding of a component of the reaction mixture. The surfaces of the capillary are smooth or have grooves running parallel or perpendicular to the flow of the sample. The different speed of flow of the reagents is achieved with the aid of gaps, and the variation in the size of the respective gaps modifies the capillarity in the gap and, consequently, the flow of the reaction mixture.
Test elements known in the prior art generally consist of vertical or horizontal structures through which a liquid sample (e.g. blood, plasma, urine) flows. Spatial separation of reagents for preliminary reactions, suppression reactions (e.g. vitamin C suppression), enrichment of substances, or reagent separation because of incompatibility in these test elements is made possible by a vertical structure of reagent layers (for example impregnated tissues, papers, membranes or microporous films). In a horizontal structure, different reagent zones, assembled or discretely impregnated, can be produced one behind the other. However, control of the dwell time in the respective zones or compartments has hitherto been possible only by mechanical action from outside (for example Reflotron, reaction valve). Detection of various parameters in a rapid test often demands control of the dwell time in reaction or enrichment zones, e.g. as a function of the reaction time or dissolution time. Mechanical control of this dwell time by an apparatus, however, requires a complex apparatus structure, which entails high costs.
Therefore it is one of the objects of the present invention is to make available a test element which avoids the disadvantages of the prior art.